1. Field of the Invention
This invention relates to an improved process of extraction of gallium from aqueous solutions thereof to provide for recovery of the gallium in a very pure form either as the metal or as the hydroxide. In particular the process involves a double extraction and strip or scrub stages employing a different extractant in each extraction stage and an acidic strip stage after the first extraction and a basic strip stage after the second extraction. The first extraction involves the use of an alkylated 8-hydroxyquinoline extractant while the second extraction employs an amine extractant. The extraction process is a liquid-liquid process in which the water insoluble extractant compounds are employed in a water insoluble, water immiscible, organic solvent. Due to the immiscibility the organic phase can be separated from the aqueous solutions treated.
2. Descriotion of Related Art
Extraction of gallium from aqueous solution by liquid-liquid extraction systems has been carried out in the past. U.S. Pat. No. 3,637,711 dascribes the recovery of metal values from aqueous solutions with an organic solvent containing hydrocarbyl substituted 8-hydroxyquinolines such as allylbenzyl or .beta.-alkenyl substituted 8-hydroxyquinolines. While directed primarily to the recovery of copper, gallium is one of the metals listed for recovery.
U.S. Pat. No. 3,971,843 describes the recovery of gallium present in aqueous solution which may also contain a compound of aluminum and sodium. In this process the aqueous solution is contacted with a substituted hydroxyquinoline in an organic solvent immiscible with water and under highly alkaline conditions whereby gallium, sodium and aluminum, when present, are extracted. The gallium can be separated from the sodium and aluminum by contacting the organic phase with a dilute solution of an inorganic acid to remove sodium and aluminum from the organic phase and then contacting the organic phase with a more concentrated solution of inorganic acid to remove the gallium.
U.S. Pat. No. 4,169,130 describes the recovery of gallium values from highly basic aqueous solutions thereof, especially from sodium/aluminum liquors of Bayer process origin, by liquid/liquid extraction with a water immiscible organic phase comprising an organic solvent and a dissolved, water insoluble substituted hydroxyquinoline. The recovery is characterized in that at least the step of extracting the gallium values is conducted under an inert atmosphere.
In U.S. Pat. No. 4,241,029 gallium values are recovered from the basic aqueous solutions thereof, especially from sodium/aluminum liquors of Bayer process origin, by liquid/liquid extraction with a water immiscible organic phase comprising an organic solvent and dissolved therein, an organic solvent soluble, substituted hydroxyquinoline and an organic carboxylic acid compound.
In a paper, Solvent Extraction Ion Exchange, 2, 1984 pp. 45-69, "The Extraction of Zn II, Pb II and Gallium III from Alkaline Solutions by Alkylated Hydroxyquinoline. T. Sato, T. Nakamura and H. Oishi, the extraction of Zn.sup.+2, Pb.sup.+2 and Ga.sup.+3 from sodium hydroxide solutions by Kelex 100, an alkylated hydroxyquinoline, in kerosene has been carried out under differing conditions. It is shown that these metals are extracted effectively from alkaline solutions by Kelex 100.
In Hydrometallurgy, 16 (1986), pp. 315-324 "Solvent Extraction of Galium III from Sodium Hydroxide Solution by Alkylated Hydroxyquinoline." T. Sato and H. Oishi, the distribution equilibria and kinetics of the extractions of Gallium III from sodium hydroxide solutions by 7-(5,5,7,7-tetramethyl-1-octen-3-yl)-8-hydroxyquinoline, Kelex 100, designated HQ, in kerosene have been examined under various conditions. From the dependence of the distribution coefficient on the concentrations of aqueous hydroxide and Kelex 100 it is deduced that the extraction can be expressed as Ga(OH).sub.4 (a) +3HQ(o).revreaction.GaQ.sub.3 (a) + OH-(a) +3H.sub.2 O(a). Furthermore, the kinetic results suggest that Ga(III) is taken up through the formation of either of two different activated species, Na.sup.+ [Ga(OH).sub.3 ], OH and Na.sup.+ .multidot.Na.sup.+ [Ga(OH).sub.3 ], depending on the concentration of sodium hydroxide in the aqueous phase.
In Journal Inorganic Nuclear Chemistry, 24, pp. 321-327, (1964), "Extraction of In (III) and Ga (III) From Aqueous Chloride Media By Long Chain Alkyl Amines and Quaternary Salts." M. L. Good and F. F. Holland, Jr., the extraction of Ga.sup.+3 and In.sup.+3 from aqueous chloride systems by long chain alkyl amines and high molecular weight quaternary salts in organic solvents has been studied using tracer techniques. The effects observed with respect to change in organic diluent, amine type and acid concentration in the aqueous phase, parallel those seen previously during similar investigations of aqueous chloride systems of Co.sup.+2 and Fe.sup.+3. However, the In.sup.+3 system appears to be unique in that the stoichiometry of the extracted species in the case of a tertiary amine seems to be different from that obtained with a quaternary salt. The results indicate that the ratio of amine to In.sup.+3 is 2:1 in the extracted species obtained with tertiary amines and is 1:1 for the quaternary salt solutions. An extracted species for Ga.sup.+ 3 containing a GaCl.sup.4- entity is indicated in both amine and quaternary salt systems.
In Journal Inorganic Nuclear Chemistry, 27, pp. 2429-2436, (1965), "Analysis Of the Halide Complexes of Fe (III), Co(II), Ga (III) And In(III) Extracted From Aqueous Chloride Media By High Molecular Weight Substituted Alkyl Ammonium Compounds, M. L. Good and S. C. Srivastava, a complete analysis (including infra-red spectroscopy) has been made on the organic extract solutions obtained when Fe.sup.+3, Co.sup.+2, Ga.sup.+3 or In.sup.+3 is extracted from aqueous chloride solutions by a high molecular weight quaternary ammonium salt or an amine hydrochloride in an inert diluent. The results are compared with the deductions make about the nature of the extracted metal entities from equilibrium extraction data. For these metals it is shown that the extracted entity contains the tetrahedral tetrachloride anion in all cases. No evidence is found for extraction of acidic metal-chloride species.
In Solvent Extraction and Ion Exchange, 2 (2), pp. 201-212 (1984), "Liquid-Liquid Extraction of Gallium (III) From Hydrochloric Acid Solutions By Organophosphorus Compounds And High Molecular Weight Amines", T. Sato, T. Nakamura and S. Ishikawa, the extraction of Ga.sup.+3 from hydrochloric acid solutions has been investigated using organophosphorus compounds (tributylphosphate, trioctylphosphine oxide and di-(2-ethylhexyl)-phosphoric acid) and high molecular weight amine (trioctylamine and trioctylmethylammonium chloride). The equilibrium expressions are proposed on the basis of the distribution data.
In Hydrometallurgy, 4, pp. 285-290, (1979), "Liquid-Liquid Extraction of Gallium By Tri-n-Butyl Phosphate", A. DeSchepper, the recovery of gallium from discarded germanium plant solutions by solvent extraction with tri-n-butyl phosphate (TBP) has been investigated. Because of the high content of iron, selective extraction of gallium with undiluted TBP is not possible, but suitable conditions are obtained by diluting the TBP with an aliphatic hydrocarbon and extracting at an acidity of 4M. It is advantageous to reduce the Fe.sup.+3 in the initial solution to Fe.sup.+2. Scrubbing of the loaded organic phase with HCl also increases the final Ga/Fe ratio. Gallium can then be recovered from the strip solution by hydrolysis.